What is different at Belle II?

Transcription

1 From Hadron Colliders to e+e What is different at Belle II? LHCb Workshop LMU Munich 1

2 Location Item PEP-II Tevatron LEP LHC (Super)KEKB Page 2

3 KEK Tsukuba Tokyo e+ e Narita Mt. Fuji Page 3

4 KEKB Accelerator Continuous injection Luminosity 8.0 GeV e3.5 GeV e+ Page 4

5 Crab Cavities 22 mrad crossing angle between beams Rotate bunches to have head-on collisions Page 5

6 KEKB Performance Design World record luminosity: 2.1 x 1034 cm-2s-1 Twice design 1 ab-1 of integrated luminosity Page 6

7 World Record Luminosity Item Lmax = 2.1 x 1034 cm-2s-1 Page 7

8 B Factory e+e Y(4S) B0B0 (50%) B+B- (50%) σ = 1.05 nb Continuum background σ = 3.70 nb Page 8

9 Production of B Mesons HadronCollider: pp, pp Belle CDF Strong interaction of quarks/gluons in hadrons: B Factory: e+e Electromagnetic interaction of elementary particles: High rate Known kinematics Production of all kinds of b hadrons in fragmentation BB events from Y(4S) decays without background tracks Page 9

10 B0 Reconstruction In Y(4S) CMS: B0 e+ E*beam E*beam e- B0 Energy and momentum of B mesons determined by beam energy Page 10

11 Continuum Suppression Fox-Wolfram moments: Hk = Σij pi pj Pk(cos θij), Pk: Legendre pol. Cleo cones B momentum/thrust direction Vertex separation Δz Page 11

12 Measurement of CP Violation Golden Mode: B0 J/ψ K0 Time dependent asymmetry measurement: Page 12

13 Measurement of time-dep. CP Violation Flavor of initial state, time of decay m(y(4s))= GeV, 2 x m(b) = GeV p*(b) 300 MeV B mesons almost at rest in center of mass system (CMS) B Y(4S) B B meson flight distance in CMS too small for a time measurement Page 13

14 Measurement of time-dep. CP Violation + Asymmetric beam energies - l+ B0sig Y(4S) e- K0S e+ z B0tag Entanglement + - s - K+ Decay of one B meson at time ttag in flavor eigenstate Q tagging Other B meson is at time ttag in flavor eigenstate Q Time measurement: t = tsig - ttag = z / c Page 14

15 Flavor Tagging + Only opposite side tagging (no fragmentation) l+ B0sig Y(4S) e- K0S e+ All remaining particles are from the tag B meson + z B0tag - - s - K+ Leptons, high momentum particles, kaons, Lambdas, slow pions (from D*) Tagging power: εd2 30%, D = 1-2w, w: wrong tag fraction Page 15

16 Observation of CP Violation PRL 108, (2012) 772 x 106 BB B0 B0 B (cc) KS B J/ψ KL Observation of mixing-induced CP violation in B0 system Confirmation of KM mechanism of CP in the Standard Model Page 16

17 Full Reconstruction π ν K D π Btag Y(4S) Bsig K Full reconstruction of one ν hadronically decaying B meson Momentum and charge of signal B meson known All remaining particles belong to signal B meson Reconstruction of decays with neutrinos Page 17

18 B K(*) Rare FCNC decay without long range effects ( no direct CPV) Theoretically reliable SM prediction: BR(B+ K+ ) = (4.0 ± 0.5) x 10-6 BR(B0 K*0 ) = (9.2 ± ) x 10-6 Buras et al., JHEP 1502, 184 (2015) Sensitive to new physics Page 18

19 New Physics in B K(*) B K* C L/R: left/right handed Coupling B Xs B K FL SM Fraction of longitudinal K* polarization NP Altmannshofer et al, JHEP 0904, 022 Page 19

20 Search for New Invisible Particles Same experimental signature of B K(*) and B K(*) + invisible particles (S) Can be distinguished from K if new particles have mass B KSS B K Requires measurement of q2 = m2( ) q2 / mb2 JHEP 0904, 022 Page 20

21 Analysis Technique Reconstruction of hadron + other B meson hadronic or semileptonic or inclusive tag nothing else in the detector extrapolation with MC Signal region No further energy in the calorimeter SM x20 EECL, Eextra = sum of clusters energies not assigned to hadron or tag B Sideband region PRL99, Page 21

22 B K(*) Results arxiv: Page 22

23 Full Event Interpretation Huge number of B meson decay modes Hierarchical reconstruction Multivariate classifiers Per mill level efficiency Page 23

24 Belle II: Aim For 50 ab-1 SuperKEKB 8 x 1035 cm-2 s-1 Page 24

25 Accelerator Design: Nano Beam Scheme Invented by Pantaleo Raimondi for SuperB y ( y*/ y) Page 25

26 SuperKEKB Upgrade Belle II New IR e- 2.6 A New beam pipe & bellows New superconducting /permanent final focusing quads near the IP e+ 3.6 A TiN-coated beam pipe with antechambers Replace short dipoles with longer ones (LER) Low emittance positrons to inject Damping ring Add / modify RF systems for higher beam current Redesign the lattices of HER & LER to squeeze the emittance Positron source New positron target / capture section Low emittance gun Low emittance electrons to inject Page 26

27 Belle II Detector Challenges KEKB SuperKEKB Higher background radiation damage, occupancy Higher event rate trigger, DAQ, computing Low momentum particle reconstruction and ID, hermeticity Detector has to be upgraded for SuperKEKB conditions to achieve equal or better performance than at KEKB Page 27

28 Belle II Detector Compared with Belle Page 28

29 Belle II Detector TDR: arxiv: KL and muon detector: EM Calorimeter: CsI(Tl), waveform sampling (barrel) Pure CsI + waveform sampling (end-caps) Resistive Plate Counter (barrel) Scintillator + WLSF + MPPC (end-caps) Particle Identification electrons (7GeV) Time-of-Propagation counter (barrel) Prox. focusing Aerogel RICH (fwd) Beryllium beam pipe 2cm diameter Muon detector positrons (4GeV) Vertex Detector 2 layers DEPFET + 4 layers DSSD Magnet Central Drift Chamber He(50%):C2H6(50%), small cells, long lever arm, fast electronics Velocity detector Muon Photon Charged particle Tracking Calorimeter Page 29

30 Beam Pipe and Pixel Detector Beryllium beam pipe r = 1.0 cm Vertex Detector 2 layers DEPFET r = 1.4 and 2.2 cm Significant improvement in vertex resolution Belle Belle II Page 30

31 Silicon Strip Detector Belle II Belle Improvement in δs(ksπ0γ) because of larger KS acceptance (by ~30%) Vertex Detector 4 layers DSSD r = cm Page 31

32 Drift Chamber Belle Belle II Reduced dead time because of new electronics 1-2 μs 200 ns Central Drift Chamber He(50%):C2H6(50%), small cells, long lever arm, fast electronics Better momentum resolution because of larger outer radius Page 32

33 Barrel Particle ID Barrel Particle Identification Time-of-Propagation counter Compact design, Improved K/π separation Simulation p = 2 GeV/c, θ = 90 deg Page 33

34 Endcap Particle Identification Endcap Particle Identification Prox. focusing Aerogel RICH Improved K/π separation Testbeam Page 34

35 EM Calorimeter EM Calorimeter: CsI(Tl), waveform sampling (barrel) Pure CsI + waveform sampling (end-caps) Better signal to background separation because of wave form sampling and pure CsI in endcaps Page 35

36 KL and Muon Detector KL and muon detector: Resistive Plate Counter (barrel) Scintillator + WLSF + MPPC (end-caps) Replacement of RPCs in endcaps and inner barrel layers with scintillators to tolerate high background rates Page 36

37 Belle II Collaboration ~700 members 100 institutions 23 countries Page 37

38 BEAST II: Background Measurements Page 38

39 SuperKEKB First Turns Page 39

40 SuperKEKB / Belle II Schedule Page 40

41 Search for New CP Violating Phases Page 41

42 Search for Right-Handed Currents B0 K*0 ( KS π0) γ 5 ab-1 SM: SCP = 2 (ms/mb) sin(2ϕ1) 50 ab-1 Values up to 0.7 sin(2ϕ1) possible in left-right symmetric NP models Page 42

43 Direct CP in B Kπ B0 vs. B0 Sum rule: Bvs. B+ now 50 ab-1 A(K0 0): 0.15 A(K0 0): Page 43

44 Search for Multiple Higgs Bosons World average of R(D), R(D*) 4.0σ away from SM pred. Incompatible with 2HDM of type II Page 44

45 More New Physics Searches Lepton flavor violation CP violation in D0 mixing 1, 2, 50 ab-1 B( ) 90% CL upper limit [10-9]: 45 (~0.5 ab-1) 5 (50 ab-1) Precision of q/p : 0.16 (~0.5 ab-1) 0.05 (50 ab-1) Page 45

46 Y(5S) Physics Absolute Bs BRs, Spectroscopy (Zb discovery) Page 46

47 Summary e+e Y(4S) BB em. interact.: ~1 nb Boost βγ 0.4 Known kinematics No background tracks Good neutrals rec. Full event interpret. Decays with neutrals Inclusive decay rates Absolute BRs Charm, τ, Y(5S), spectroscopy Isidori, Nir, Perez Ann.Rev.Nucl.Part.Sci 60, 355 (2010) Page 47